A heat storage material, particularly a supercooling latent heat storage material, utilizes the heat to absorb and dissipate a large amount of latent heat at a certain temperature, during the process of melting and solidification. A heat storage material containing sodium acetate trihydrate as a main material is used for heating and calefaction in a medium temperature region, and a heat storage material containing sodium sulfate decahydrate as a main material is used for cooling and refrigeration in a low temperature region.
However, when simple sodium acetate trihydrate is used as a main material, thermal energy storage stability is deteriorated. This is because precipitation of anhydrous sodium acetate (anhydrate) that does not function as a heat storage material occurs, and when the material is repeatedly used, the effect of this anhydrate is further increased. Thus, various measures for preventing this precipitation have been investigated.
For example, a method of gelling a heat storage material by adding xanthan gum, which is one kind of polysaccharides (see Patent Literature 1), and addition of water (see Patent Literatures 2 and 3) have been proposed. However, when it is required to use the heat storage material at a temperature far lower than −20° C., for example, in automotive applications, when it is required for the heat storage material to maintain a supercooled state at a temperature near −30° C. and to retain thermal energy storage stability, these methods have been not necessarily satisfactory. In the case of the addition of xanthan gum, the crystallization temperature does not drop that much, while in the case of the addition of water, there is a problem that if the amount of addition is small, the crystallization temperature is high; and if the amount of addition is large, the amount of heat dissipation is small. Furthermore, a method of adding sodium thiosulfate pentahydrate as a means for maintaining a supercooled state at a low temperature (see Patent Literature 4) has also been proposed; however, the method has a problem that the rate of crystallization is slow.